Various antenna element and antenna array configurations are utilized in wireless communications today. The dipole antenna, for example, is one of the most commonly encountered antenna configurations today. Their simplicity makes them relatively inexpensive and easy to build and deploy. As such, the dipole antenna is probably the most widely used form of antenna element in various mobile and base station installations.
Generally speaking, a dipole antenna element gives only 2.13 dBi of gain. Accordingly, many current manufacturers of wireless systems will use a pair of dipoles, such that the gain increases to about 5 dBi. For example, an antenna array may be configured in which pairs of dipole antenna elements are disposed above a ground plane to provide a desired level of gain and a radiation pattern having a desired contour/directivity.
The patch antenna is another antenna configuration found in wireless communication systems today. A patch antenna element comprises a piece of metal plate sized according to a desired operating frequency band. Although providing increased gain over that of a dipole antenna element, patch antenna elements are fairly large in size, as compared to a dipole antenna element responsive to the same frequency band. Moreover, patch antennas often require complicated manufacturing processes and/or assembly techniques in order to provide a useful antenna array.
It is sometimes desirable to provide a base station or access point having dual-band performance. For example, it may be desirable to accommodate wireless communications operating according to different protocols, such as advanced mobile phone service (AMPS) and personal communication service (PCS), utilizing different frequency bands, such as 800 MHz and 2.4 GHz. Additionally or alternatively, particular wireless devices may utilize more than a single frequency band, such as to access more than a single service. For example, depending on the services required, a wireless device may have an operating frequency of 2.4 GHz and 5.2 GHz. As such, antennas should be provided which are efficient in these two bands in order to provide optimum transmission and reception of radio signals.
One prior technique for providing a dual-band antenna configuration is to provide an antenna array aperture having antenna elements responsive to each such band interleaved therein. For example, dipole elements responsive to a first frequency band may be disposed in columns having dipole elements responsive to a second frequency band, therebetween. Such a configuration effectively provides two single band antenna systems in a single antenna array. Accordingly, a relatively large number of antenna elements are utilized and a relatively complex antenna configuration results. Moreover, the antenna feed network in such a dual-band configuration may be complex or otherwise undesirable. For example, separate low loss (and expensive) antenna feed cables may be required by each such interleaved antenna array.
Alternatively, dual-band dipole antenna elements having a single feed may be realized using a load. Specifically, a load may be placed in each element of the dipole, to act as a low or high impedance at the respective frequency of interest, to provide dual-band performance. However, frequency optimization often results in adjusting current paths and, in most cases, involves impedance matching of the required bands. Such dual-band dipole elements can be relatively expensive and complicated to design and produce.
Another technique for providing a dual-band antenna configuration has been to utilize the aforementioned patch antenna elements. For example, different modes may be set on a patch antenna to give it dual-band performance. However, the use of such dual-band modes further complicates the design and manufacture of such elements. Moreover, such antenna elements remain relatively large. Accordingly the use of patch antenna elements may not be desirable in particular dual-band systems.